Enrico Guastaldi

A new FSA approach for in situ γ ray spectroscopy.

An increasing demand of environmental radioactivity monitoring comes both from the scientific community and from the society. This requires accurate, reliable and fast response preferably from portable radiation detectors. Thanks to recent improvements in the technology, γ spectroscopy with sodium iodide scintillators has been proved to be an excellent tool for in-situ measurements for the identification and quantitative determination of γ ray emitting radioisotopes, reducing time and costs. Both for geological and civil purposes not only (40)K, (238)U, and (232)Th have to be measured, but there is also a growing interest to determine the abundances of anthropic elements, like (137)Cs and (131)I, which are used to monitor the effect of nuclear accidents or other human activities. The Full Spectrum Analysis (FSA) approach has been chosen to analyze the γ spectra. The Non Negative Least Square (NNLS) and the energy calibration adjustment have been implemented in this method for the first time in order to correct the intrinsic problem related with the χ(2) minimization which could lead to artifacts and non physical results in the analysis. A new calibration procedure has been developed for the FSA method by using in situ γ spectra instead of calibration pad spectra. Finally, the new method has been validated by acquiring γ spectra with a 10.16 cm × 10.16 cm sodium iodide detector in 80 different sites in the Ombrone basin, in Tuscany. The results from the FSA method have been compared with the laboratory measurements by using HPGe detectors on soil samples collected particular, the (137)Cs isotopes has been implemented in the analysis since it has been found not negligible during the in-situ measurements.

A multivariate spatial interpolation of airborne γ-ray data using the geological constraints

In this paper we present maps of K, eU, and eTh abundances of Elba Island (Italy) obtained with a multivariate spatial interpolation of airborne γ-ray data using the constraints of the geologic map. The radiometric measurements were performed by a module of four NaI(Tl) crystals of 16 L mounted on an autogyro. We applied the collocated cokriging (CCoK) as a multivariate estimation method for interpolating the primary under-sampled airborne γ-ray data considering the well-sampled geological information as ancillary variables. A random number has been assigned to each of 73 geological formations identified in the geological map at scale 1:10,000. The non-dependency of the estimated results from the random numbering process has been tested for three distinct models. The experimental cross-semivariograms constructed for radioelement-geology couples show well-defined co-variability structures for both direct and crossed variograms. The high statistical correlations among K, eU, and eTh measurements are confirmed also by the same maximum distance of spatial autocorrelation. Combining the smoothing effects of probabilistic interpolator and the abrupt discontinuities of the geological map, the results show a distinct correlation between the geological formation and radioactivity content. The contour of Mt. Capanne pluton can be distinguished by high K, eU and eTh abundances, while different degrees of radioactivity content identify the tectonic units. A clear anomaly of high K content in the Mt. Calamita promontory confirms the presence of felsic dykes and hydrothermal veins not reported in our geological map. Although we assign a unique number to each geological formation, the method shows that the internal variability of the radiometric data is not biased by the multivariate interpolation.

First characterisation of natural radioactivity in building materials manufactured in Albania

This study focuses on the radiological characterisation of building materials manufactured in Albania by using a high-resolution gamma-ray spectrometer. The average activity concentrations of (40)K, (226)Ra and (232)Th were, respectively, 644.1±64.2, 33.4 ± 6.4 and 42.2 ± 7.6 Bq kg(-1) in the clay brick samples and 179.7 ± 48.9, 55.0 ± 5.8 and 17.0 ± 3.3 Bq kg(-1) in the cement samples. The calculated activity concentration index (ACI), varied from 0.48±0.02 to 0.63±0.04 in the clay brick samples and from 0.29±0.03 to 0.37±0.02 in the cement samples. Based on the ACI, all of the clay brick and cement samples were categorised as A1 materials. The authors can exclude (at 3σ level) any restriction of their use as bulk materials.

Total natural radioactivity, Tuscany, Italy

In this paper, we report an extensive survey of the natural radioactive content of rocks of the Tuscany Region (Italy): this permitted the first total natural radioactivity map of the region. The sampling was planned using the geological map of Tuscany at scale 1:250,000, which contains 45 distinct geological groups recognized by tectonic and stratigraphic features. Each geological group was characterized for the total activity by measuring the activity concentrations of 40K, 238U and 232Th in 865 samples using a high-purity germanium (HPGe) gamma-ray spectrometer. The average areal distribution of samples is approximately one sample per 25 km2. The radiometric map was constructed through the reclassification of each geological formation based on the median value of the total activity. Seven classes of total activity are identified by choosing percentiles almost evenly spread across the range of values. This map represents the starting point for future studies on natural background radiation, geochemical processes and epidemiological investigations.

Total natural radioactivity, Veneto (Italy)

We present the first detailed map of the terrestrial natural radioactivity of the Veneto Region (Italy), a 18,264 km2 densely populated area, previously investigated through indoor radon surveys. The activity concentration in 709 representative samples of the main Alpine lithostratigraphic units was measured by using a high-purity germanium (HPGe) γ-ray spectrometer to characterize the radioactivity content of the 41 cartographic units of the Veneto Lithostratigraphic map at 1:250,000 scale. An area accounting for 61% of the territory, comprising alluvial plains was investigated through airborne γ-ray measurements. The large-volume NaI detectors were mounted on an ultralight aircraft, flying a 7000 km line. The data were interpolated using Ordinary Kriging, and a distribution model of the radioactivity content was produced. The result of the data analysis is a total natural radioactivity map of Veneto at 1:250,000 scale in which the activity concentration of the territory is visualized in seven classes, according to the percentile values calculated on the total dataset of measurements.

Three-dimensional reconstruction of the Carrara Syncline (Apuane Alps, Italy): An approach to reconstruct and control a geological model using only field survey data

This paper presents an approach to reconstruct geological structures in three dimensions using and honouring field survey geological data. The methodology was developed to reconstruct the poly-deformed Carrara Syncline (Apuane Alps, Italy) in order to better understand the relationships regarding the structural geology of the area and the hydrogeological fluxes. In the first step, all the geological data (observed, measured and interpreted) of the study area were organized in a database using a geographical information system. The standard tools of a computer-aided design (CAD) environment were used to build geological profiles using the observed data (outcropping contact lines) extracted from the database, as well as, to create the contact surfaces via interpolation using non-uniformal rational B-spline surfaces. The intersection lines between each of these surfaces and the digital elevation model yield the model contact lines (MCLs). Discrepancies between the MCLs and the corresponding outcropping contact lines were analysed to further constrain the surfaces of the model. Starting from these surfaces, a voxel-based solid model was built, for storing and displaying each rock formation.

Risk analysis for remediation of contaminated sites: the geostatistical approach

The assessment of the risks associated with contamination by elevated levels of pollutants is a major issue in most parts of the world. The risk arises from the presence of a pollutant and from the uncertainty associated with estimating its concentration, extent and trajectory. The uncertainty in the assessment comes from the difficulty of measuring the pollutant concentration values accurately at any given location and the impossibility of measuring it at all locations within a study zone. Estimations tend to give smoothed versions of reality, with the smoothing effect being inversely proportional to the amount of data. If risk is a measure of the probability of pollutant concentrations exceeding specified thresholds, then the variability is the key feature in risk assessment and risk analysis. For this reason, geostatistical simulations provide an appropriate way of quantifying risk by simulating possible “realities” and determining how many of these realities exceed the contamination thresholds, and, finally, provides a means of visualizing risk and the geological causes of risk. This study concerns multivariate simulations of organic and inorganic pollutants measured in terrain samples to assess the uncertainty for the risk analysis of a contaminated site, an industrial site in northern Italy that has to be remediated. The main geostatistical tools are used to model the local uncertainty of pollutant concentrations, which prevail at any unsampled site, in particular by means of stochastic simulation. These models of uncertainty have been used in the decision-making processes to identify the areas targeted for remediation.

Uranium distribution in the Variscan Basement of Northeastern Sardinia

ABSTRACT We present a detailed map of uranium distribution and its uncertainties in the Variscan Basement of Northeastern Sardinia (VBNS) at a scale of 1:100,000. An area of 2100 km2 was investigated by means of 535 data points obtained from laboratory and in situ gamma-ray spectrometry measurements. These data volume corresponds to the highest sampling density of the European Variscides, aimed at studying the genetic processes of the upper crust potentially triggered by an enrichment of radiogenic heat-producing elements. For the first time, the Kriging with Variance of Measurement Error method was used to assign weights to the input data which are based on the degree of confidence associated with the measurements obtained using different gamma-ray spectrometry techniques. A detailed tuning of the model parameters for the adopted Experimental Semi-Variogram led to the identification of a maximum distance of spatial variability coherent to the observed tendency of the experimental data. We demonstrate that the obtained uranium distribution in the VBNS, characterized by several calc-alkaline plutons emplaced within migmatitic massifs and amphibolite-facies metamorphic rocks, is an excellent benchmark for the study of ‘hot’ collisional chains. The uranium map of VBNS, and in particular the Arzachena minor pluton, confirms the emplacement model based on the recognition of the different petrological associations characterizing the Variscan magmatic processes in the Late Paleozoic. Furthermore, the presented model of the uranium content of the geological bedrock is a potential baseline for future mapping of radon-prone areas.

Geostatistical Modeling of Uncertainty for the Risk Analysis of a Contaminated Site

This work is a study of multivariate simulations of pollutants to assess the sampling uncertainty for the risk analysis of a contaminated site. The study started from data collected for a remediation project of a steel- works in northern Italy. The soil samples were taken from boreholes excavated a few years ago and analyzed by a chemical laboratory. The data set comprises concentrations of several pollutants, from which a subset of ten organic and inorganic compounds were selected. The first part of study is a univariate and bivariate sta- tistical analysis of the data. All data were spatially analyzed and transformed to the Gaussian space so as to reduce the effects of extreme high values due to contaminant hot spots and the requirements of Gaussian simulation procedures. The variography analysis quantified spatial correlation and cross-correlations, which led to a hypothesized linear model of coregionalization for all variables. Geostatistical simulation methods were applied to assess the uncertainty. Two types of simulations were performed: correlation correction of univariate sequential Gaussian simulations (SGS), and sequential Gaussian co-simulations (SGCOS). The outputs from the correlation correction simulations and SGCOS were analyzed and grade-tonnage curves were produced to assess basic environmental risk.

Approccio multi-isotopico ed idrogeochimico per la caratterizzazione di acque termali: il caso di Saturnia (GR)@@@Multi-isotope and Hydrogeochemical approach for characterizing Saturnia thermal groundwater (Grosseto, Italy)

Aim of this study is to define the groundwater flow of thermal area of Saturnia, through both chemical and isotope analyses. After a first detailed geological-geophysical survey and a quantification of the available groundwater resources, we analyzed several chemical compounds (Na, Ca, Mg, K, Chlorides, Sulfates, Nitrates, total alkalinity, Li, Sr, B, Fluorides, soluble Silica, free Carbon Dioxide, Sb, As, Se, H2S, Fe, Mn, Hg e Pb) and isotopes (2H; 3H, 3He, 4He, 13C, 18O, 86Sr, 87Sr). Excluding the uncertainties mainly related to a large repetition of measures over time, we concluded the following conclusions. Both Lithium and Boron high values and 87Sr/86Sr values highlighted that “Calcare Cavernoso” limestone geological formation constitutes the Saturnia thermal aquifer. Such samples showed both the same chemical characteristics and source area. Boron, Lithium, δ2H, δ18O and 87Sr/86Sr show the Saturnia thermal aquifer is separated by those of Pitigliano (Latera- Bolsena thermal circuit) and Bagni San Filippo (Mt. Amiata thermal circuit). 18O, 3H e δ13C measured in samples coming from Saturnia thermal spring respectively indicate that water feeding the thermal aquifer infiltrate at 350-440 m a.s.l., that they are almost 30 years old, and finally they that are isolated regarding to external infiltration. Low value of R/Ra tends to exclude the influence of Earth mantle to the geothermal anomaly of Saturnia area. The high content in Selenium indicates a possible interaction between Saturnia spring water and those coming from the Saturnia well, with volcanic fluids. However, considering also the evidence of the separation between the Saturnia groundwater flow and those of neighboring thermal fields (Bolsena and Mt. Amiata), we hypothesized that only a exchange among these volcanic complexes and the source area of thermal water points exists, but not among these complex and Saturnia aquifer.